How to Convince Clients of the Need for Heartworm Preventatives

PARAMUS, N.J. — Sometimes owners give veterinarians a hard time about prophylaxis against heartworm, but Dwight D. Bowman, MS, PhD, said it isn’t too hard to convince them of the need if veterinarians talk about the disease the worms cause.

“Heartworms are a foot long,” he said here at Oradell Animal Clinic during one of the stops for the CAPC Road Show, an educational tour sponsored by the Companion Animal Parasite Council. “They’re not little itty, dinky bacterial things. They’re giant worms that live in the pulmonary arteries of dogs.”

Clinical signs of heartworm disease depend on the stage of infection; but in later stages, infection with Dirofilaria immitis can cause cough, exercise intolerance, dyspnea, hepatomegaly, syncope, ascites, and abnormal heart and lung sounds. If left untreated, the dog can die.

“You find them in the heart of a dead dog, which is why they’re called heartworms,” said Bowman, who is professor of parasitology at Cornell University College of Veterinary Medicine. “They sit in the pulmonary artery, and every time the heart beats, they go donk, donk, donk against the wall [causing damage].”

This is definitely one of those diseases that is easier to prevent than treat, he added. “Prevention is such an easy sell. If you really think about the alternatives, there’s no reason not to have preventatives,” he said, adding that all of the preventatives are excellent products.

“We [at CAPC] believe in year-round treatment of dogs and cats with broad-spectrum heartworm anthelmintics that have activity against parasites of zoonotic potential,” Bowman said. “And we believe in annual testing for canine heartworm.”

Part of the problem with controlling heartworm in many parts of the United States might not be convincing clients about the need, but convincing veterinarians that heartworm is prevalent in all 50 states and that prophylaxis should be year-round, according to Bowman.

However, recent data presented at the NAVC Conference earlier this year provided pretty convincing evidence: Dogs across the United States tested positive for heartworm. The data were collected by IDEXX Laboratories as part of a voluntary national veterinary reporting system. Most results were based on testing with the company’s SNAP 3Dx and 4Dx in-clinic tests.

At least 3 million dogs were sampled beginning in 2000. The survey found that 3.9% of dogs tested positive for heartworm antigen in the Southeast, compared with 0.8% in the Midwest, 0.6% in the Northeast and 1.2% in the West. “We calculated that if there were only 50 million dogs in the United States, 683,500 were infected with heartworms. And we’re sampling well-cared-for pets. These are not shelter dogs. These are dogs that went to a vet,” Bowman said.

The number of positive tests in the West surprises many veterinarians who believe that heartworm is not a factor in the western states. “We have some really high [infection] areas in California, and California doesn’t believe it at all,” he said.

“When I was born, there wasn’t any heartworm out West. None. Zero,” he admitted, but with the interstate highway system and more people traveling with their pets, heartworm has traveled across the country and even into Canada.

The American Heartworm Society did another survey in 2005 and found a similar distribution as the IDEXX data.

The case for year-round prevention also might seem like a hard sell at first, he said, but that shouldn’t be either.

Thanks to global climate change, many states experience longer bouts of warm weather and shorter bouts of cold. The USDA recently changed its seasonal maps for agriculture because outdoor temperatures have changed the planting times.

Even in areas with lots of snow, he has seen the occasional mosquito in the winter, Bowman said, and told the story of one Christmas in Ithaca, N.Y. “Mosquitoes can be active in warm winters,” he said. “I was at a Christmas party. A bunch of us were having fun. And this mosquito started to chase me around the kitchen, so I chased it back. I ran around, caught the mosquito as it tried to bite me on the arm, and raced to the lab to dissect it.

“My kids wanted to stay at the party, foolish as they were. They thought that would be more fun than going with dad to the lab. But this is a typical Bowman Christmas,” he joked.

This mosquito was one of the many that carry D. immitis, but “unfortunately [the mosquito] did not have heartworm [organism] because that would have been the best Christmas ever,” he said.

The current system to prevent heartworm in the United States is not working, according to Bowman, because dogs continue to become infected. “I believe it’s a lack of year-round prophylaxis everywhere,” he said. “You are preventing severe lung and heart disease that impairs the quality of life and is a potential threat to someone else’s pet,” he said.